The invention relates to a card especially suited for manufacturing nonwovens for the production of air laid fibrous webs formed aerodynamically, comprising fiber feed means, a driven main cylinder rotating at a high speed, an air shaft or passage which, within the area of the fiber doffing zone, extends substantially tangentially to the main cylinder and as far as to an air-permeable nonwovens web conveying means and suction means arranged beneath the nonwovens web conveying means, the centrifugal force at the main cylinder throwing the fibers in the fiber doffing zone into the air current generated in the air passage and adapted to transport the fibers to the nonwovens conveying means to deposit them as a fibrous web, and a process for the aerodynamic formation of a fibrous web comprising the following steps:
1. applying fibers to a driven cylinder rotating at a high speed;
2. throwing the opened fibers within the area of a fiber doffing zone from the cylinder into an air current; and
3. conveying the fibers into the air current to an air-permeable nonwovens conveying means and separating the fibers from the air current on the nonwovens conveying means.
Such nonwovens cards for the production of aerodynamically formed fibrous webs have been known for instance from U.S. Pat. No.(s). 4,064,600, 4,130,15 and EP-A-0 093,585.
In case of the nonwovens card disclosed in U.S. Pat. No. 4,097,965, compressed air is blown into the air shaft or air passage extending substantially tangentially to the main cylinder, said compressed air being rerouted within the range of the main cylinder by a deflecting plate to radially strike on the main cylinder. As a result thereof, upon their exit from the carding area, fibers are not detached directly from the main cylinder, but they are separated from the latter at a certain delay entailing a displacement of the fiber doffing zone. Air current used with said nonwovens card is sharply deviated repeatedly and air current homogeneity is affected accordingly. Above all, due to the deviation of the air current at the deflecting flap in a direction containing a component counter to the sense of rotation of the main cylinder, strong turbulences of the conveying air are caused which impair the uniformity of the fibrous web deposited on the nonwovens conveying means.
U.S. Pat. No. 4,130,915 relates to an improvement of the foregoing nonwovens card in which the air shaft extends only as far as to the main cylinder, said air shaft being provided, if necessary, with compressed air, while, in addition, a segment of the carding region, is exposed to a pressure between 150 and 400 mm Ws at an air current of 28m.sup.3 /(min.m).
EP-A-0 093,585 discloses a nonwovens card in which a turbulent air current is generated in an air shaft extending tangentially to the main cylinder, said air shaft hardly constricted cross-sectionally, comprising in the fiber doffing zone a sharp kink increasing the turbulence of the air current.